In conventional wireless receiving devices, a preamble signal at the head of a frame is received to thereby demodulate a control signal included in the preamble signal. By this process, parameter elements applied to a data portion subsequent to the preamble portion can be grasped to appropriately demodulate a data signal in the data portion.
However, frames are received not always beginning with their leading portions, and there may be a case where no preamble signal is received. In this case, the mode (structure) of each frame cannot be determined, which makes it difficult to perform appropriate demodulation. To avoid it, there is a method of determining the mode of a received signal, utilizing the features (such as the length, interval and cycle of a known signal) of frames corresponding to respective modes assumed for the signal.